May-June 2012

U.S. Weather Highlights 2011: Unparalleled Weather Extremes

by Douglas LeComte

The deadliest tornado outbreak in over 70 years, deadliest single tornado in over 60 years, record flooding in the Missouri and Mississippi Valleys, devastating heat and drought in the South, the “Groundhog Day Blizzard,” Hurricane Irene, “Snowtober”… the list goes on and on. The number of extreme weather events in 2011 may have been without precedent, as the National Climate Data Center for the first time ever tallied 14 billion-dollar weather-related disasters in a single year.

Snow and Cold

A strong La Niña (cold waters in the eastern tropical Pacific) and persistently negative Arctic oscillation (blocking polar high pressure) drove the weather patterns early in the year, resulting in the cold and snowy winter across the northern United States and the intensification of drought across the South.

Although the Washington, D.C.-Philadelphia corridor missed out on major snows during early 2011, winter's fury did not spare other parts of the nation, and near-record snows buried the western mountains, Rockies, the Midwest, the Northeast, and even the South. The entire eastern two-thirds of the United States experienced below-normal temperatures during December 2010-February 2011.

The cold and storms resulted in abundant snow cover. Following a Deep South snowstorm on January 9–10, every state in the Union except Florida measured snow on the ground, and 69 percent of the contiguous United States was snow-covered on January 11.

The southern low that dumped four to six inches of snow on the Atlanta area tracked northward along the East Coast on January 11–12, bringing the second major snowstorm to the Northeast in just over two weeks. In Massachusetts, winds gusting to 46 mph accompanied Boston's 11.6 inches of snow, and gusts to 61 mph lashed Nantucket. To the west of Boston, Sturbridge measured 23.0 inches of snow, and the Berkshires saw as much as 30.0 inches. In Connecticut, Hartford saw an all-time record snowfall of 24.0 inches—its greatest since records began in 1905.

Another coastal low on January 26-27 dumped 19.0 inches of snow on New York City, with most of the I-95 corridor from Washington, D.C., to Boston picking up 6-12 inches. This storm was enough to break New York City's January snowfall record, bringing the total up to 36.0 inches and shattering the mark set in 1925 (27.4 inches). For Hartford, Connecticut, this snow (13.9 inches) brought its monthly total to 56.9 inches. No other month of record has even come close.

The January storms, along with the late December 2010 Nor'easter, contributed to the all-time snowiest season in parts of the Northeast. Hartford, Connecticut, for example, totaled 86.4 inches by spring—nearly twice its long-term average.

This winter also saw notable cold waves. An Arctic outbreak on January 21 caused temperatures to plummet to −46°F at International Falls, Minnesota. Bitter cold made its way to the Northeast on January 24, when Bennington, Vermont, registered −22°F and Glens Falls, New York, dropped to −30°F.

Of the many storms that affected the nation this winter, “credit” for the greatest national impact goes to the January 31-February 2 “Groundhog Day Blizzard.” On February 1, snow and dangerous wind chills extended from Colorado to the Great Lakes. As the associated low tracked northeastward, an expansive area of wintry weather covered large parts of the nation, with the National Weather Service posting winter storm warnings and watches from New Mexico to New England. Blizzard conditions reached Chicago that night, with winds gusting to 61 mph. The storm stranded around 1,000 motorists on Lake Shore Drive and led to the cancellation of over 1,300 flights in Chicago. Nationwide, the storm caused the cancellation of some 6,000 flights and affected 100 million people across 2,000 miles. The 20.2-inch, three-day snowfall in Chicago made this the city's biggest February storm on record and its third-largest storm of any month. Total United States losses from this event are estimated at greater than $1.8 billion, with 36 deaths.

Another memorable snowstorm buried an area from Northeast Oklahoma to Northwest Arkansas with 15-25 inches on February 8-9. A report of 25.0 inches in Oklahoma set a new state record for 24-hour snowfall. The extreme cold that followed the storm (−31°F) established a new Oklahoma record.

Tragic Spring

March was abnormally wet, from the Pacific Northwest to the Dakotas and along the Ohio River through New England. An active storm track in April, combined with snowmelt, triggered widespread flooding from Washington State to New England. In May, the Mississippi River reached levels not seen since the Depression era.

This was the wettest April in 117 years of recordkeeping from Illinois to West Virginia. Farther west, Montana notched its second-wettest November-April period. Thirty-day rainfall totals up to May 11 exceeded 15 inches over southeast Missouri through Southern Illinois, Western Kentucky, and Southern Indiana.

As a result, the Mississippi and lower Ohio rivers rose to major flood levels by the first half of May. On May 8, the Mississippi peaked at 58.53 feet at Cairo, Illinois—the highest level since 1937. The crest at Memphis, Tennessee, on May 9-10 of 47.87 feet was more than 13 feet above flood stage, and also the highest since 1937. Although the river submerged outlying areas of Memphis, the city center escaped flooding. Other areas were not as fortunate, and floodwaters submerged three million acres by May 11 in Mississippi, Arkansas, and Tennessee. On May 14, the Army Corps of Engineers opened the Morganza Spillway in Louisiana for the first time since 1973 to relieve flooding pressures on New Orleans and Baton Rouge, which were inundating farmland across central Louisiana. Total estimated economic losses for the flooding range from $3 to $4 billion.

The flooding shared the headlines with other historic severe weather this spring. April was simply the most extraordinary month for severe weather ever recorded, with 758 tornadoes and 43 killer tornadoes taking 360 lives. The weather maps showed a repeating sequence of events: upper air low pressure systems and jet streams plunging southward into the Central United States and tropical moisture streaming northward from the Gulf, fueling severe thunderstorm development.

During the first outbreak of the month, severe weather spread from Texas to Pennsylvania and south to Florida on April 3-5. On April 4, there were more than 1,300 reports of wind damage—a one-day record. On April 4-5, a line of thunderstorms produced 46 tornadoes, contributing to a three-day toll of nine fatalities and over $2.8 billion in estimated damage.

The second major outbreak of this historic month spread damage mainly from Texas to Wisconsin on April 8-11. Fifteen tornadoes struck Wisconsin on April 10, one of which wiped out part of the town of Merrill. This outbreak caused some $2.2 billion in estimated damage.

The April 14-16 outbreak focused on the South. An EF3 tornado on April 15 caused major damage near Jackson, Mississippi. On April 16, a tornado tore through Raleigh, North Carolina. This twister and others took 24 lives in North Carolina, and the death toll from the three-day outbreak totaled 38. In all, 177 tornadoes struck the region, causing damages estimated at $2.1 billion.

The historic April 25-28 event began with a cold front that triggered tornadoes in Arkansas, leading to eight fatalities. On April 26, an area of severe weather spread from Eastern Texas to Kentucky, including 60 tornadoes across eight states. The twisters that tracked across the South on April 27 were large, numerous, and deadly. By daybreak on April 28, 316 people had died. The EF4 that roared across Alabama on April 27 destroyed much of Tuscaloosa, taking 64 lives, and went on to wreck the western suburbs of Birmingham. The associated super cell traveled over 300 miles and spawned twisters across Northern Georgia and the Carolinas. A separate EF5 that tore across Northwestern Alabama and into Tennessee was so powerful that it ripped the bark off of trees and tossed a Corvette over 671 feet.

The 316 deaths on April 27 made this the deadliest tornado day since 1925. One hundred twenty-two tornadoes tracked across parts of Mississippi, Alabama, Tennessee, Virginia, and Georgia that tragic day. During the four-day outbreak, more than 2,400 people were injured, and the property damage exceeded $10.2 billion.

May actually started out relatively tranquil, with the Mississippi flooding being the principal concern. But tornadoes developed in Oklahoma on May 22 and tracked into Missouri. The EF5 that ripped across Joplin, Missouri, wiped out over half of the city, caused 158 deaths and 1,150 injuries, and damaged or destroyed 7,500 homes. This was the deadliest single twister since 1947, and one of the six deadliest on record. The six-day outbreak from May 22-27 hammered states from Oklahoma to Pennsylvania, causing over $9.1 billion in losses.

Severe storms even struck New England. On June 1, an EF3 tornado tracked through Springfield, Massachusetts, killing three, injuring 72, and leaving extensive damage in its 39-mile wake. This was likely the most destructive twister to strike New England since the Worcester storm of 1953.

Severe drought in the Southwest, Southern Plains, and Southeast damaged crops and raised the wildfire danger. Fires blazed across the south from Arizona to Florida. A fire that developed in late May in Eastern Arizona (the “Wallow Fire”), started by a campfire and fanned by strong winds, grew into a monster that scorched 538,000 acres, destroying 32 homes. This was the largest fire ever documented in Arizona. New Mexico also experienced its largest fire of record, with the Las Conchas blaze scorching more than 150,000 acres. In September, the Bastrop Fire southeast of Austin, Texas, destroyed 1,500 homes, making this the most destructive fire in Texas history. In Texas alone, fires burned more than three million acres this year.

Flooding, Heat, and Drought

Ample snow pack in the West and the excessive water from the inevitable melt continued to be a flood concern for the West and Midwest well into spring. Significant flooding in Montana due to frequent rains and snow melt led to downstream flooding of the Missouri River to June and beyond. Eastern Montana flooding from May 22 to June 21 displaced 1,100 residents. In North Dakota, flooding of the Souris River left 15-20 percent of Minot under water by June 24, affecting 4,000 homes and forcing the evacuation of an estimated 11,000 residents. The Souris was at record stage until July 4. Water from the Missouri River across the Upper Midwest overflowed numerous levees, flooding thousands of acres of farmland. Estimated losses from the Upper Midwest flooding this spring and summer exceed $2 billion.

Persistently cool weather dominated the Northwest through spring, but high temperatures over the Southwest and South in spring and summer severely aggravated drought, and threatened other parts of the nation as well. Already in early June, triple-digit temperatures (103°F on June 7 at Minneapolis-Saint Paul) spread northward and eastward to the Upper Midwest and the mid-Atlantic—a harbinger of what was to come.

Heat was the big story in July for much of the nation. The Southern Plains recorded its hottest July in more than a century. Oklahoma, Kansas, and Texas were ground zero for the most intense heat. In Oklahoma City, every day except two from June 23 through July 18 saw thermometers climb to 100°F. The heat peaked on July 9 with a reading of 110°F, the third-highest temperature ever recorded. At Wichita Falls, Texas, temperatures soared to 111°F on June 17 and 18, and July 9.

The area of triple-digit heat that covered the Central and Southern Plains during the first half of the month expanded mid-month into the Upper Midwest and then swelled eastward to the Atlantic coast, resulting in a mega heat wave from July 16 to 22.

By July 17, temperatures in the mid-90s to 100°F or above extended from North Dakota to Texas and eastward to Illinois and Wisconsin. Dew point temperatures in the high 70s to low 80s spread across the Upper Midwest, creating dangerous heat indices well above 100°F. On July 19, the heat index in Minneapolis-Saint Paul reached a remarkable 119°F, thanks to a record dew point of 82°F.

In Chicago, the heat wave culminated with back-to-back readings of 99°F at O'Hare Airport on July 20-21, and the heat and humidity made it to the East Coast on July 21-23. On July 22, essentially every urban area from the Carolinas to New Hampshire experienced triple-digit heat, and the humidity made this one of the most oppressive days of record in the mid-Atlantic. All-time temperature records were established in Newark, New Jersey (108°F); Hartford, Connecticut (103°F); Washington-Dulles, Virginia (105°F); and Bridgeport, Connecticut (103°F). Urban heat indices of 110°F to 120°F extended from South Carolina to New York. This was the hottest July and hottest month ever at Washington, D.C., and Baltimore, Maryland.

Severe storms did not vanish during the late spring and summer. A June 18-22 severe weather outbreak over the Midwest and Southeast caused over $1.3 billion in losses; a derecho tracked across Northern Illinois on July 11, damaging thousands of trees and leaving 850,000 customers without power; a haboob roared across Arizona on July 5, shutting down the city of Phoenix, Arizona; and a severe thunderstorm on August 13 caused a music stage to collapse at the Indiana State Fair in Indianapolis, taking seven lives.

August saw little to no respite from the heat firmly established across the Texas area. Dallas-Fort Worth counted 40 consecutive days of triple-digit heat, ending on August 11. This was the second longest streak of consecutive 100-degree days, falling just two days short of the record set in 1980.

Top 10 U.S. Weather Events 2011

Tornado Super Outbreak. During April 25–28, the largest tornado outbreak on record, with 343 twisters, raked five states across the Southeast. On the deadliest day, April 27, 122 tornadoes killed 316 people, including 240 in Alabama. This was the third deadliest outbreak in United States history, and total losses exceeded $10.2 billion.

Southern Plains Drought. Persistent dry weather from October 2010 through September 2011 accompanied by searing summer heat resulted in the worst Southern Plains drought since the mid-1950s and the worst 12-month drought in Texas history. The drought destroyed crops and grasslands, dried up water supplies, killed millions of trees, and set the stage for massive wildfires. Estimated losses to farmers and ranchers approached $10 billion.

Joplin Tornado. Part of a six-day outbreak that caused more than $9.1 billion in losses, the EF5 tornado that destroyed part of Joplin, Missouri, on May 22 took 158 lives, injured 1,150, and damaged or destroyed 7,500 homes. This was the deadliest single tornado since 1947.

Mississippi and Ohio River Flooding. The wettest April in 117 years of recordkeeping from Illinois to West Virginia helped to trigger major flooding in May. The Mississippi River rose to 13 feet above flood stage at Memphis, Tennessee, and floodwaters ultimately submerged three million acres in Mississippi, Arkansas, and Tennessee leading to losses estimated at $3 to $4 billion.

Record Summer Heat Southern Plains. Texas, Oklahoma, New Mexico, and Louisiana experienced their hottest summer on record, with Oklahoma statewide temperatures the highest of any state for any summer of record. Oklahoma City, Oklahoma, suffered through 63 days with triple-digit heat, while Dallas-Fort Worth counted 71 and Houston 46—all breaking records set during the 1980 heat wave.

Hurricane Irene. Irene crossed the Virgin Islands and Puerto Rico on August 21–22 and then made landfall as a Category 1 storm in North Carolina on August 27. She tracked northward along the mid-Atlantic coast, making landfall over New York City as a tropical storm on August 28 before continuing through New England. The storm left over five million homes and business without power and triggered major flooding across the Northeast from New Jersey to Vermont. At least 45 people died, and damages reached some $7.3 billion.

Northern Plains and Missouri River Basin Flooding. Heavy rain and melting snow caused the Missouri River to overflow in June, flooding thousands of acres of farmland. Flooding of the Souris River in North Dakota inundated 4,000 homes in Minot, forcing 11,000 residents to evacuate.

Mid-April Tornado Outbreak. One of the largest outbreaks on record took place during April 14–16, as 177 tornadoes swept across an area stretching from Oklahoma to North Carolina. The outbreak caused 38 deaths, including 24 in North Carolina, with damages estimated at $2.1 billion.

“Snowtober” Nor'easter. The intense coastal storm on October 29–30 combined with unseasonably cold air to produce the largest October snowstorm the Northeast has experienced in over a century, and possibly two centuries. Immense damage to trees from snowfalls that ranged from 4–30 inches caused power outages for more than three million homes and businesses.

Groundhog Day Blizzard. On February 1–2, the Midwest experienced one of the most severe blizzards on record. Chicago's snowfall of 20.2 inches was the third greatest in more than 100 years. The storm stretched from the Plains to New England, and was blamed for 36 deaths and losses exceeding $1.8 billion.

This summer's heat, along with the spring and summer dryness, transformed the Southern Plains drought into one of the most intense of all time. In short, it was the hottest summer (June-August) on record in Texas, Oklahoma, New Mexico, and Louisiana. This was also the driest spring and driest summer in Texas. The drought ravaged crops, dried up water supplies, killed millions of trees, and contributed to massive wildfires. Although centered in Texas, the drought also included parts of New Mexico, Oklahoma, and Louisiana, and extended eastward through Georgia.

Considering intensity and duration, the 2011 drought could be considered the worst for Texas since the mini-dust bowl drought of the mid-1950s, and the most intense 12-month and summertime drought on record. Direct losses to farmers and ranchers due to the drought across the Southern Plains and Southwest have been estimated to approach $10 billion.

Active Tropical Storm Season

The Atlantic tropics were again active this year, with 19 storms of tropical storm strength or greater.

Hurricane Irene became the first hurricane to strike the United States mainland since Hurricane Ike hit Galveston in 2008. Irene crossed the Virgin Islands and Puerto Rico on August 21-22, cutting power to over 800,000 households in Puerto Rico. The storm made landfall near Cape Lookout in North Carolina on August 27 as a minimal Category 1, and then tracked northward along the coasts of Maryland, Delaware, and New Jersey, making landfall over New York City as a tropical storm on August 28. The storm continued northward through New England, bringing powerful winds and battering waves to coastal areas, and flooding rains to New York and interior New England. Extensive power outages affected a dozen states (five million homes and businesses), and major flooding spread across the region, particularly from New Jersey through New York and Vermont. Floodwaters in Vermont destroyed roads and bridges, isolating 13 communities. The storm was blamed for 45 deaths across the East, and total damages reached some $7.3 billion.

Tropical Storm Lee made landfall in Louisiana on September 3-4, and its remains tracked northeastward though the Tennessee and Ohio Valleys, dumping heavy rain from the Gulf Coast into New York. “Training” thunderstorms dropped immense amounts of rain from September 6-8 on the mid-Atlantic. Ten to 15 inches or more fell from Virginia and Maryland into Pennsylvania, setting off major flooding. Parts of the Susquehanna River Basin in New York and Pennsylvania experienced the worst flooding on record.

Snowtober

The Northeast racked up its third historic storm in three months as a Nor'easter on October 29 combined with abnormally cold air to bring widespread snow from West Virginia to Maine. Amounts of 4-10 inches were common, but totals of 15-30 inches extended from Northern Connecticut into New Hampshire. For October, nothing in the past century (and, perhaps, two centuries), including the freakish October snowstorms of 1987 and 1979, appears to exceed this storm in extent, intensity, and impact. The damage to trees still bearing leaves from Northern New Jersey into Connecticut was enormous. In Connecticut, the storm left some 800,000 homes and businesses without power—the largest power outage in state history. Total customers losing power across the Northeast exceeded three million.

Ironically, much of the nation experienced a dearth of snow during November-December, with Alaska being the big exception. The Bering Sea superstorm lashed the west coast of Alaska on November 8-9. The 943-mb (27.85 inches) low pressure system brought heavy snow, hurricane-force winds, and 40-foot waves to the region during what appears to be the most intense storm to strike that coast since 1974.

A cold wave and major snows affected other parts of Alaska in November, with Fairbanks' thermometers unable to rise above 0°F from November 14-22. Immense snows buried the south coast of the state in November and December, with Valdez measuring 66.4 inches in November and a staggering 152.2 inches in December.

The year ended with some relief for at least parts of the country. October-December rain and snow relieved some of the worst drought in the Southern Plains, despite the return of La Niña, which usually means dry weather across the South. According to the United States Drought Monitor, severe drought in Texas dropped from 71 percent coverage in early October to 53 percent in early January 2012.